MELATONIN RHYTHMS AND PINEAL STRUCTURE IN A TROPICAL BAT, ANOURA-GEOFFROYI, THAT DOES NOT USE PHOTOPERIOD TO REGULATE SEASONAL REPRODUCTION

It has been hypothesized that pineal structure and function might diff er between temperate zone and tropical species of mammals because of l ower amplitudes of seasonal change in photoperiod and, in some areas, less seasonal climatic variation. Anoura geoffroyi produce a single of fspring in November or December of each year on the Caribbean island o f Trinidad, at 10 degrees N latitude in the deep tropics. Previous wor k has shown that this population lacks reproductive responses to photo period, and must be enforcing seasonal breeding using a non-photoperio dic cue. Anoura geoffroyi have a minute, thin, and rod-like pineal gla nd. Throughout much of its length, the pineal courses irregularly with in the ventrolateral wall of the great cerebral vein. This intimate re lationship may have functional implications. Despite having a very sma ll pineal gland, this species produced a nocturnal rise in serum melat onin. Serum melatonin levels in most individuals were below or near un detectable levels during the light period and rose to a peak averaging 100 pg/ml in the last third of the dark period. Our results indicate that, although the pineal gland of A, geoffroyi is extremely small, se rum melatonin levels are comparable to those of other mammals.